Ahh, there's your problem. The ScanGauge does need to make some assumptions since it isn't measuring fuel flow directly. (Don't ask me for details...I don't know.) You need to go into the Setup and change the parameters to match the engine of the vehicle with which you are using it. It is probably set to gas by default, but the displacement may well be wrong. The procedure is detailed in your manual if you have it handy. If not you can probably figure out out on your own, or one of us can help you out. (I would just walk you through it now but I don't remember the procedure without being in front of it.)